Soil moisture is important for plant growth. A lack of moisture content over a growing season is a good indicator of drought, which can have social, environmental, and economic impacts. Increasing temperatures and changes in rainfall patterns are expected to increase the frequency and intensity of drought in many regions. Growing season soil moisture deficits are estimated by the potential evapotranspiration deficit, the difference between rainfall and evapotranspiration.

This layer shows the standardised annual soil moisture (potential evapotranspiration deficit (PED)) across New Zealand for 1988 as part of the data series for years 1972 to 2013.

Evapotranspiration is the loss of water by evaporation and plant transpiration. PED is the difference between estimated evapotranspiration and rainfall.

We produced maps of the standardised annual PED (the departure from the 1981–2010 average, divided by the 1981–2010 standard deviation) were produced for every growing season (calculated as July–June years) from 1972 to 2013.

Care should be taken when comparing maps from year to year – days may be missing from the PED GIS data, and data may have been interpolated to complete the dataset. The interpolation accuracy is lowest in areas of high elevation, where there are fewer climate stations and complex terrain affects accuracy. Climate stations may also open and close, affecting the accuracy of the data provided.

This dataset relates to the "Soil moisture and drought" measure on the Environmental Indicators, Te taiao Aotearoa website.